Protectors for electric circuits



Dec. 8, 1970 A. URANI PROTECTORS .FOR ELECTRIC CIRCUITS Filed June 26, 1968 United States Patent 3,546,661 PROTECTORS FOR ELECTRIC CIRCUITS Angelo Urani, St. Louis, Mo., assignor to McGraw-Edison Company, Elgin, 111., a corporation of Delaware Filed June 26, 1968, Ser. No. 740,246 Int. Cl. H01r 13/68, 33/06 US. Cl. 339132 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in prong-equipped panels.

It is, therefore, an object of the present invention to provide an improved prong-equipped panel.

It is customary to equip radio sets and television sets with prong-equipped panels that can receive the female plugs of the line cords of those sets. Those prongequipped panels are usually mounted on the chassis of those radio and television sets, and those female plugs are usually mounted on the removable walls of those sets; and the removal of those removable walls automatically separates those female plugs from those prong-equipped panels. The prongs of those prong-equipped panels are intended to receive power from the female plugs of the line cords of the radio and television sets, and hook-up wires extend between those prongs and the power-consuming components of those radio and television sets to supply power to those power-consuming components. In some radio sets, and in most television sets, circuit-protecting devices such as electric fuses or circuit breakers are connected between the prongs of the prong-equipped panels and the power-consuming components. If the circuit breakers could be depended upon to open the circuits when overloads of predetermined size and duration developed, and if the owners of radio and television sets would not use over-size electric fuses, the circuit-breakers and electric fuses in radio and television sets would open the circuits of those sets before'any of the hook-up wire could fuse. Unfortunately, however, circuit breakers can not always be depended upon to open the circuits when overloads of predetermined size and duration develop, and the owners of radio and television sets have been known to use over-size electric fuses when electric fuses of the correct rating have not been immediately available or when relatively high resistance grounds have developed and have caused those radio and television sets to draw more than their rated currents. Inasmuch as hook-up wires are made quite small in diameter to minimize the cost thereofthe hook-up wires in a radio or television set can tend to fuse if that radio or television set draws more than its rated current and that radio or television set is equipped with a circuit breaker or with an oversize electric fuse. Any fusing of the hookup wires would be very objectionable because it could lead to the development of exposed electrical arcs; and any fusing of the hook-up wire between the prong-equipped panel and the circuit breaker or electric fuse would be even more objectionable, because it could lead to the development of exposed electrical arcs which could not be "ice halted by the circuit-breaking action of the circuit breaker or electric fuse. The present invention virtually prevents any and all fusing of the electrical connection between the prong-equipped panel and the circuit breaker or electric fuse of a radio set, television set or other electronic device; and it does so by providing a prong-equipped panel with a fuse socket and by connecting one of the prongs of that panel and one of the terminals of that socket by a conductor which has a current-carrying capacity greater than that of any electric fuse which can be connected in series with that electronic device by means of that socket. As a result, if an overload that develops in a radio set, television set or other electronic device which uses one of the prong-equipped panels of the present invention, the circuit of that electronic device will be broken where it should be broken, namely, within the housing of the circuit breaker or within the casing of the electric fuse. It is, therefore, an object of the present invention to provide a prong-equipped panel for a radio set, a television set or other electric device with a fuse socket and to connect one of the prongs of that panel and one of the terminals of that socket by a conductor which has a current-carrying capacity greater than that of any electric fuse which can be connected in series with that electric device by means of that socket.

The fuse socket, of the prong-equipped panel provided by the present invention, is mounted so the electric fuse held by that fuse socket can be removed and replaced without any need of removing the removable wall of the radio set, television set or other electronic device. This is very desirable; because it enables the owner of that radio set, television set or other electronic device to replace a fuse that has opened in response to a transient overload-and thus enables that owner to avoid the cost and delay involved in a service call by a radio, television or electronic technician. However, the fuse socket of that prong-equipped panel is mounted so close to the prongs of that prong-equipped panel that the female plug of the line cord, into which those prongs will extend, will make it difficult for a person to wrap one or more of his or her fingers around the insulated knob which must be gripped and rotated to remove the electric fuse from that socket. This is important; because it will keep very small children from being able to apply strong enough forces to the knob, which must be gripped and rotated to remove the electric fuse from that socket, to free that electric fuse from that socketand thus will keep such small children from inserting a finger in that socket and touching the live contact therein. It is, therefore, an object of the present invention to provide a prong-equipped panel which has a fuse socket mounted so close to the prongs of that prong-equipped panel that the female plug of the line cord, into which those prongs will extend, will make it difiicult for a person to wrap one or more of his or her fingers around the insulated knob which must be gripped and rotated to remove the electric fuse from that socket.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of the present invention is shown and described, but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. 1 is a front elevational view of one preferred embodiment of prong-equipped panel that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is a side elevational view of the prong-equipped panel shown in FIG. 1,

FIG. 3 is a rear elevational view of the prong-equipped panel shown in FIG. 1,

FIG. 4 is a sectional view, on a larger scale, through the prong-equipped panel of FIG. 1, and it is taken along the plane indicated by the line 44 in FIG. 1,

FIG. 5 is another sectional view, on the scale of FIG. 4, through the prong-equipped panel of FIG. 1, and it is taken along the plane indicated by the line 55 in FIG. 3,

FIG. 6 is yet another sectional view, on the scale of FIG. 4, through the prong-equipped panel of FIG. 1, and it is taken along the plane indicated by the line 66 in FIG. 2,

FIG. 7 is a front elevational view, on the scale of FIG. 4, of part of the prong-equipped panel of FIG. 1, as that prong-equipped panel appears when the electric fuse is removed, and it is taken along the plane indicated by the line 7-7 in FIG. 4,

FIG. 8 is a further sectional view, on the scale of FIG. 4, through the prong-equipped panel of FIG. 1, and it is taken along the plane indicated by the line 88 in FIG. 4,

FIG. 9 is a perspective view of the stationary contact of the fuse socket of the prong-equipped panel of FIG. 1, and

FIG. 10 is a longitudinal section through one end of a preferred form of electric fuse that is usable with the prong-equipped panel provided by the present invention.

Referring to the drawing in detail, the numeral denotes a panel which can be secured to the chassis of a radio set, a television set or any other electronic device. That panel will be made from insulating material; and, preferably, will be made from a readily-moldable, insulating material. A generally rectangular recess 22 is formed in the outer face of that panel; and that recess is dimensioned to accommodate the recessed face of the female plug of a line cord. The numeral 24 denotes an annulus of insulating material which has a reduced thickness rim at the inner face thereof, and that rim is disposed within a cylindrical recess 25 in the outer face of the panel 20. That annulus is close to the rectangular recess 22, as shown by FIGS. 1 and 4; and it projects outwardly from the outer face of that panel. The numeral 26 denotes a hollow cylinder which has the left-hand end thereof disposed within a cylindrical recess 27 in the right-hand face of the panel 20, as that cylinder and that panel are viewed in FIGS. 4 and 6. The inner end of that cylinder projects to the right from the right-hand face of that panel; and that hollow cylinder is coaxial, and in communication, with the annulus 24. In fact, that annulus effectively acts as a largerdiameter forward extension of that hollow cylinder. The numeral 28 denotes reduced-thickness upper and lower edges on the panel 20; and those edges facilitate the mounting of that panel in an opening in a wall or bracket of the chassis of a radio set, television set or other electronic device. Openings 30 are provided in the reduced-thickness upper and lower edges 28; and those openings will accommodate rivets, screws, bolts or other fasteners, not shown.

The numeral 34 denotes a stationary contact which is made of metal and which is mounted within the annulus 24 adjacent the reduced-thickness rim at the inner face of that annulus. That stationary contact has a circular opening 36 therein; and generally rectangular notches 37 in that stationary contact are contiguous with that circular opening. The circular opening 36 is dimensioned to accommodate the projecting end of a cylindrical contact 55 'which is supported by an insulating knob 56; and that insulating knob is preferably molded onto, and thus made integral with, the cylindrical contact 55. Laterally-extending ears 54 are provided on the projecting end of the cylindrical contact 55, and the notches 37 are dimensioned to accommodate those ears. A generally flat spring 57 is disposed within the cylindrical contact 55, and that spring tends to act as a chord of that contact. However, that spring can yield to assume an arcuate configuration which is complementary to the arcuate configuration of the inner surface of cylindrical contact 55. The insulating knob 56 is dimensioned to telescope freely within the annulus 24; and the outer end of that knob is formed with fiat sides, as shown particularly by FIGS. 1 and 6, to facilitate the gripping and rotating of that knob and of the cylindrical contact carried thereby.

The notches 37 are located at the opposite ends of a diameter of the stationary contact 34, and the ears 54 on the cylindrical contact 55 are located at the opposite ends of a diameter of that cylindrical contact. As a result, whenever the ears 54 on the cylindrical contact 55 are aligned with the notches 37 in the stationary contact 34, the inner end of that cylindrical contact can be passed through the opening 36 and those cars can be passed through those notches. Thereafter, when the insulating knob 56 is rotated about its geometric axis, the ears 54 on the cylindrical contact 55 will rotate into position beneath the opening-defining portions of the stationary contact 34, and will prevent accidental separation of that cylindrical contact from that stationary contact. However, separation of the cylindrical contact 55 from the stationary contact 34 can easily be effected by rotating that cylindrical contact until the cars 54 thereon are in register with the notches 37 in that stationary contact, and by moving that cylindrical contact outwardly through the annulus 24.

A movable contact 38 has a terminal-receiving portion at one end of the shank thereof, and that terminalreceiving portion is disposed 'wholly within the hollow cylinder 26. That shank extends through an opening in the end wall of the hollow cylinder 26 and has a perforated, planished end; and that perforated, planished end is disposed wholly exteriorly of that hollow cylinder. A helical compression spring 39 surrounds that portion of the shank of the movable contact 38 which is disposed within the hollow cylinder 26; and that spring urges the terminal-receiving portion of that movable contact toward the stationary contact 34. However, the perforated, planished end of the movable contact 38 is larger than the diameter of the opening in the end wall of the hollow cylinder 26; and hence that perforated, planished end will limit the extent to which that movable contact can move toward the stationary contact 34.

The numerals 40 and 42 denote prongs which are mounted within spaced openings in the panel 20; and those prongs extend forwardly and outwardly through the recess 22. Those prongs are spaced apart so they can be engaged by the female plug of the line cord of a radio set, television set or other electronic device. The inner end of the prong 42 is planished and has an opening therein as shown by FIG. 2; and that prong is staked or otherwise deformed to rigidly lock it in position relative to the panel 20. The prong 40 has a reduced-diameter inner end, as shown by FIG. 5; and that inner end extends through an opening in a conductor 46 and is then riveted over. That conductor is preferably made integral with the stationary contact 34, as shown by FIG. 9. That stationary contact also has a securing ear 44 thereon; and that stationary contact, the conductor 46, and the securing ear 44 can be made integral by punching them out of a single piece of metal. Solder or other electrical bonding material Will be applied to the conductor 46 and to the riveted-over inner end of the prong 40 to make certain that a low resistance connection is provided between that conductor and that prong.

The securing ear 44 and the conductor 46 will initially lie in the plane of the stationary contact 34, as indicated by solid lines in FIG. 9. However, before that stationary contact is assembled with the panel 20, that ear and that conductor will be bent rearwardly until they lie in planes that are parallel to each other, that are spaced apart a distance equal to the outer diameter of the stationary contact '34, and that are disposed at right angles to the plane of that stationary contact. The rearwardly-bent ear 44 on the stationary contact 34 will be passed through an opening 58 in the panel 20, and will then be bent downwardly into locking position within a recess 60 in the rear face of that panel to help secure that stationary contact in assembled relation with that panel. The rearwardly-bent conductor 46 on the stationary contact 34 will be passed throughan opening 62 in the panel 20, and will then be bent upwardly along the rear face of that panel to help secure that stationary contact in assembled relation with that panel. The conductor 46 is disposed at one side of the stem of a T-shaped partition 64 which is integral with and which extends 'rearwardly from the inner face of the panel and the planished inner end of the prong 42 is disposed at the opposite side of the stem. The cross bar of that T-shaped partition will act as an insulating barrier between the planished inner end of prong 42 and the conductor 46 and any metal wall or bracket in which the panel 20 is mounted.

After the stationary contact 34 has been fixedly secured to the panel 20, the reduced-thickness rim at the inner end of the annulus 24 will be telescoped into the cylindrical recess 25 in the outer face of the panel 20;

and a suitable glue, cement or bonding material will be used to fixedly secure that annulus to that panel. The end of the shank of the movable contact 38 will be passed through the geometric center of the helical compression spring 39, will be passed through the opening in the end wall of the hollow cylinder 26, and will then be planished and perforated. The left hand of the hollow cylinder 26 will be telescoped into the cylindrical recess 27 in the right-hand face of the panel 20, as that cylinder and that panel are viewed in FIGS. 4 and 6; and a suitable glue, cement or bonding material will be used to fixedly se cure that hollow cylinder to that panel.

The cylindrical contact 55 is dimensioned to accommodate the terminal 52 of an electric fuse 48, as shown by FIG. 4. When that terminal is telescoped into that cylindrical contact, the generally flat spring 57 will be bent from its chord-like configuration to its arcuate configuration; and the restorative forces within that spring will apply a holding force to the terminal 52 which will prevent accidental separation of that electric fuse from the cylindrical contact 55. As a result, whenever the terminal 52 is disposed within the cylindrical contact 55, the electric fuse 48 will move with and be supported by that cylindrical contact and the insulating knob 56. That electric fuse can, however, be readily separated from that cylindrical contact and that knob by the application of a firm, axially-directed pull to that electric fuse. The cylindrical contact 55 is dimensioned so it will accommodate and hold electric fuses having terminals of just one diameter, and will not accommodate electric fuses having terminals with larger diameters. As a result, cylindrical contact 55 will keep electric fuses, which have undesirably large current-carrying capacities, from being connected in series relation with the prong 40 by the fuse socket which is constituted by the annulus 24, the hollow cylinder 26, the stationary contact 34, and the movable contact 38.

In one embodiment of prong-equipment fuse provided by the present invention, the cylindrical contact 55 is dimensioned to accommodate fuse terminals which are onequarter of an inch in diameter, and the hollow cylinder 26 is dimensioned to enable the fuse socket to accommodate electric fuses that are one and one-quarter inches long. Because the current-carrying capacities of commercially available electric fuses, that are one and onequarter inches long and that have terminals which are one-quarter of an inch in diameter, do not exceed thirty amperes, the conductor 46 will have a current-carrying capacity greater than thirty amperes. Where that is the case, the electric fuse 48, rather than the conductor 46,

will fuse and open the circuit when one of the components of the radio set, television set or other electronic device becomes shorted to the chassis.

While a contact-equipped knob, such as the knob 56 with its cylindrical contact 55, can be used to hold an electric fuse within the fuse socket of the prong-equipped panel of the present invention, it is preferable to use an electric fuse, such as the fuse 70 shown in FIG. 10, which has laterally-directed ears 72 on the terminal 74 thereof. The fuse 70 has a second terminal, not shown, which can be identical 'to the terminal 50 of the electric fuse 48; and the terminal 74 of the fuse 70 will preferably have an insulating knob 76 molded onthe outer end thereof. The ears 72 on the terminal 74 will be dimensioned to pass through the notches 37 in the stationary contact 34 of the fuse socket or to underlie the opening-defining portions of that stationary contact to prevent accidental separation of the fuse 70 from that fuse socket.

Where an electric fuse, such as the fuse 70, has later ally-directed ears 'on the outer terminal thereof to directly engage the opening-defining portions of the stationary contact 34, the opening 36 in that stationary contact can be made smaller than the opening 36 in a stationary contact 34 which must accommodate the inner end of a cylindrical contact such as the cylindrical contact 55. The stationary contact 34, with the smaller opening 36 which receives a fuse such as the fuse 70, is very desirable; because that stationary contact will permit only fuses, such as the fuse 70, which have ears on the outer terminals thereof to be connected in series with the prong 40and the only commercially available fuses like fuse 70 are relatively low ameprage fuses. Specifically, the only commercially available fuses like fuse 70 have ampere ratings ranging up to ten amperes-well below the upper limit of the range of ampere ratings for commercially available fuses that can be held by the cylindrical contact 55. As a result, the conductor 46 which is integral with the sta tionary contact 34 that has the smaller opening 36 therein can have a smaller current-carrying capacity than does the conductor 46 which is integral with the stationary contact 34 that has an opening 36 large enough to accommodate the inner end of the cylindrical contact 55. However, in both cases, the conductor 46 which is integral with the stationary contact 34 will have a current-carrying capacity that is larger than the current-carrying capacity of every commercially available fuse which can be held in series with the prong 40 by the fuse socket of which that stationary contact is a part. This is important; because it means that the electric fuse, rather than the conductor 46, will fuse and open the circuit when one of the components of the radio set, television set or other electronic device becomes shorted to the chassis.

Not only does the conductor 46 have a current-carrying capacity that is larger than the current-carrying capacity of every commercially available fuse which can be held in series with the prong 40 by the fuse socket of which that stationary contact is a part, but that conductor is short and it is largely shielded by the panel 20 and by the T- shaped partition 64 at the inner face of that panel. As a result, there is little or no likelihood that the conductor 46 could be shorted to the chassis of a radio set, television set or other electronic device with which the prongequipped panel of the present invention is used. If desired, of course, all of the exposed portions of the conductor 24 could be overlain by insulation to further minimize the possibility of having that conductor shorted to the chassis of a radio set, television set or other electronic device with which the prong-equipped panel of the present invention is used.

In using the prong-equipped panel provided by the present invention, the assembler of the radio set, television set or other electronic device will pass rivets, screws, bolts or other fasteners through the openings 30 to secure the reduced-thickness upper and lower edges of that panel to a wall or bracket of the chassis of that radio set, television set or other electronic device. The recess 22 will be mounted in register with the female plug carried by the removable back of the radio set, television set or other electronic device; and the annulus 24 will be mounted in register with a suitable opening or notch in that removable back so the knob 56 of the fuse 48 or the knob 76 of the fuse 70 will be accessible to the owner of that radio set, television set or other electronic device. The assembler then will connect the grounded side of the radio set, television set or other electronic device to the planished inner end of prong 42, and will connect the ungrounded side of that radio set, television set or other electronic device to the movable contact 38. This means that the conductor 46 will directly connect the live prong 40 to the stationary contact 34 of the fuse socket, and that the chances of a short developing between the chassis of the radio set, television set or other electronic device and a point intermediate that prong and that stationary contact will be negligible.

The knob 56 of the fuse 48 or the knob 76 of the fuse 70 will be accessible to the owner of the radio set, television set or other electronic device, but that knob will be so close to the female plug of the line cord of that radio set, television set or other electronic device that it will be diificult for a person to wrap one or more of his or her fingers around that knob. This is important; because it will keep very small children from being able to apply strong enough forces to the knob 56 or the knob 76 to free the electric fuse 48 or the electric fuse 70 from the fuse socketand thus will keep such small children from inserting a finger in that socket and touching the stationary contact 34 therein. All of this means that the prong-equipped panel provided by the present invention makes the electric fuse 48 or 70 readily accessible to adults but makes it difficult, if not impossible, for small children to remove either of those electric fuses.

It will be noted that the inner end of the prong 42 is open and exposed, whereas the inner end of the prong 40 extends into the conductor 46. This is desirable, because it will help a repairman know which prong is the grounded prong and which prong is the ungrounded prong when he replaces the polarized male plug of the line cord. Also, the open and exposed nature of the inner end of the prong 42 will facilitate the task of an inspector who is charged with the task of checking the connections of the grounded and ungrounded leads of the radio set, television set or other electronic device. As a result, the use of the prong-equipped panel provided by the present invention makes it easier and safer to ground the chassis of a radio set, television set or other electronic device to the grounded side of the power line.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

I claim:

1. A prong-equipped panel which comprises:

a plate-like body of insulating material that has portions thereof securable to a part of the enclosure for an electrical appliance,

a plurality of prongs that are supported by said platelike body of insulating material, that project outwardly beyond the front face of said plate-like body of insulating material and outwardly relative to said enclosure for said electrical appliance, and that are dimensioned and spaced to receive the recessed end of a female plug,

a generally tubular fuse socket on said plate-like body of insulating material which projects rearwardly beyond the rear face of said plate-like body of insulating material and which has a fuse-receiving recess therein,

said fuse-receiving recess in said generally tubular fuse socket extending rearwardly to a point which 8 is located rearwardly of said rear face of said platelike body of insulating material,

said fuse receiving recess in said generally tubular fuse socket extending to, and opening at, the front of said plate-like body of insulating material,

said fuse-receiving recess in said generally tubular fuse socket being dimensioned to accommodate only electric fuses having current-carrying capacities below a predetermined value,

staid fuse socket having a stationary contact, and

a conductor which is, at least in part, disposed rearwardly of said front face of said plate-like body of insulating material and which extends between and interconnects one of said prongs and said stationary contact of said fuse socket,

said fuse socket enabling an electric fuse to be introduced into, and to be removed from, said fuse-receiving recess in said fuse socket from a position outwardly of said front face of said plate-like body of insulating material and while said plate-like body of insulating material is assembled with said part of said enclosure of said electrical a pliance,

the other of said prongs being adapted to have a conductor of said electrical appliance secured thereto and a second contact of said fuse socket being adapted to have a second conductor of said electrical appliance secured thereto, whereby said other prong and said second contact of said fuse socket effectively constitute the conductor-receiving terminals of said prong-equipped panel,

the first said conductor having a current-carrying capacity above said predetermined value,

whereby an electric fuse, that can be disposed within said fuse-receiving recess in said fuse socket and that can be electrically connected to said one of said prongs by said first said conductor and said stationary contact of said fuse socket, will have a currentcarrying capacity smaller than the current-carrying capacity of said first said conductor.

2. A prong-equipped panel as claimed in claim 1 wherein said first conductor is short, is integral with said stationary contact, and directly engages said one prong.

3. A prong-equipped panel as claimed in claim 1 wherein the front face of said plate-like body of insulating material is disposed adjacent a wall or bracket of a radio set, television set or other electric device, wherein said first said conductor is disposed adjacent the rear face of said plate-like body of insulating material, and wherein said one prong extends through said plate-like body of insulating material.

4. A prong-equipped panel which comprises:

a plate-like body of insulating material,

a plurality of prongs that are supported by said platelike body of insulating material, that project outwardly beyond the front face of said plate-like body of insulating material, and that are dimensioned and spaced to receive the recessed end of a female plug,

a fuse socket on said plate-like body of insulating ma terial, which projects rearwardly beyond the rear face of said plate-like body of insulating material and which has a fuse-receiving recess therein, adapted to accommodate the inner end of an electric fuse that is equipped with an insulating knob.

said fuse-receiving recess in said fuse socket extending to, and opening at, the front of said plate-like body of insulating material,

said fuse socket having a stationary contact, and

a conductor which extends between and interconnects one of said prongs and said stationary contact,

said fuse socket being disposed so close to said prongs that said female plug will, whenever it is telescoped over said prongs, largely keep a person attempting to remove said electric fuse from said fuse socket from wrapping a finger completely around said insulating 9 knob of said electric fuse which must be gripped and rotated to remove said electric fuse.

5. A prong-equipped panel as claimed in claim 4 wherein said fuse socket includes an annulus which projects forwardly from said front face of said plate-like body of insulating material and surrounds and encloses the part of said insulating knob which must be gripped and rotated to remove said electric fuse.

Re. 18,193 9/1931 Kollath 337--215X 10 2,733,314 1/1956 Schmidt 337214X 2,938,188 5/1960 Lazzery 339'-128X 3,238,334 3/1966 Lopasic et al 337--213X 3,287,528 11/1966 Boone 337-195 FOREIGN PATENTS 221,506 5/1959 Australia 337-245 US. Cl. X.R. 

